Subzero: Fix a bug in advanced phi lowering.

Subzero: Fix a bug in advanced phi lowering.

When a temporary is introduced to break a cycle, we neglected to update the predecessor count for one of the operands, leading to a possible assertion failure.

This problem isn't currently seen in master, but it arises when we enable register aliases, as in https://codereview.chromium.org/1427973003/ .  No changes are seen in spec2k code generation as a result of this fix.

A consistency check is added to help find future problems like this.

Also, refactored iteration over the Phi descriptor array to use range-based for loops and avoid directly indexing the array.

BUG= none
R=jpp@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=ea15bbe7cd6c569216ba9da3001e48ff8b4f192f

[Jim Stichnoth, 2015-11-09 18:15:47]

Description was changed from

==========
Subzero: Fix a bug in advanced phi lowering.

BUG= none
==========

to

==========
Subzero: Fix a bug in advanced phi lowering.

When a temporary is introduced to break a cycle, we neglected to update the
predecessor count for one of the operands, leading to a possible assertion
failure.

This problem isn't currently seen in master, but it arises when we enable
register aliases, as in XXX.  No changes are seen in spec2k code generation as a
result of this fix.

A consistency check is added to help find future problems like this.

Also, refactored iteration over the Phi descriptor array to use range-based for
loops and avoid directly indexing the array.

BUG= none
==========

[Jim Stichnoth, 2015-11-09 18:16:08]

Description was changed from

==========
Subzero: Fix a bug in advanced phi lowering.

When a temporary is introduced to break a cycle, we neglected to update the
predecessor count for one of the operands, leading to a possible assertion
failure.

This problem isn't currently seen in master, but it arises when we enable
register aliases, as in XXX.  No changes are seen in spec2k code generation as a
result of this fix.

A consistency check is added to help find future problems like this.

Also, refactored iteration over the Phi descriptor array to use range-based for
loops and avoid directly indexing the array.

BUG= none
==========

to

==========
Subzero: Fix a bug in advanced phi lowering.

When a temporary is introduced to break a cycle, we neglected to update the
predecessor count for one of the operands, leading to a possible assertion
failure.

This problem isn't currently seen in master, but it arises when we enable
register aliases, as in https://codereview.chromium.org/1427973003/ .  No
changes are seen in spec2k code generation as a result of this fix.

A consistency check is added to help find future problems like this.

Also, refactored iteration over the Phi descriptor array to use range-based for
loops and avoid directly indexing the array.

BUG= none
==========

[Jim Stichnoth, 2015-11-09 18:17:20]

stichnot@chromium.org changed reviewers:
+ jpp@chromium.org, kschimpf@google.com, sehr@chromium.org

[John, 2015-11-09 19:14:06]

lgtm

[Jim Stichnoth, 2015-11-09 19:19:16]

Committed patchset #2 (id:20001) manually as
ea15bbe7cd6c569216ba9da3001e48ff8b4f192f (presubmit successful).